Bare metal vs. RTOS?

 

With limited processor power, random-access memory, and flash memory, embedded systems are resource-constrained. In light of this, memory-optimized code is one of the primary objectives of firmware development. And what could be more effective than executing your code in a bare-metal application—that is, without any intermediary layers like an operating system—directly on hardware? As a developer, you have direct access to and control over all of the system's resources, including the processor, memory, and peripherals. Junior embedded developers—but not just juniors—share this viewpoint.

Baremetal vs RTOS

Working on bare-metal or RTOS-only projects for extended periods of time can prevent you from seeing all aspects of an issue, depending on the organization and the duties involved. I will examine the distinctions between the two strategies in this blog post.

1. What is RTOS?

The acronym for Real-Time Operating System is RTOS. I'll give a brief explanation of what an RTOS is so that you can comprehend the Real-Time portion.
Every RTOS is primarily composed of tasks and a scheduler. A task is linked to a data structure that contains crucial task information, like: A task uses a user-defined function to implement functionality.

• Task name and/or ID,
• State, usually described as Ready, Running, Blocked, and Suspended,
• Task priority,
• Stack size, RAM allocated for task’s stack operations,
• Pointer to the function that implements the functionality.

One component of RTOS that is in charge of overseeing task execution is the scheduler. Based on their current condition and priority, the scheduler is in charge of deciding which task should be carried out next. It is intended to offer deterministic task execution. This indicates that the tasks are completed on schedule and with predictable results.

 

 

2. Deterministic behavior

Deterministic behavior—that is, making sure that system actions are carried out within an acceptable time delay from the event's occurrence—is crucial for building safety-critical applications. For instance, airbags should be deployed within 15 milliseconds of the impact being detected. Critical tasks must be carried out on a precise frequency for some other applications.
To ensure deterministic behavior, the RTOS scheduler is made to carry out activities according to their states and priority, or how important or critical they are.
Deterministic applications for bare metal are also possible, but you need to guarantee the length of each operation. Because of this, it might be difficult to add new functionality to bare-metal programs while maintaining their determinism.

3. Scalability

It takes careful planning and appropriate software design to create scalable bare metal applications. Deterministic behavior is still challenging to apply.

What if writing data in a flash is a low priority task? How do you make sure that tasks with a higher priority have an opportunity to run? These problems are being addressed by RTOS. It handles task scheduling while keeping priorities in mind. Additionally, it can give resources to higher-priority processes by interrupting low-priority ones.
With the bare metal method, complicated applications may be written. However, employing RTOS, which provides the foundation required to write complex and networked programs, is much simpler.

4. So, is RTOS always the better option?

RTOS gives you the infrastructure to guarantee scalability and deterministic behavior, but it comes at the expense of using more resources. It needs a flash to hold the instructions and some RAM to keep things operating. An RTOS is a superior design option if you are working on a large linked application, but bare metal is a battery strategy if you are building a basic application with minimal capabilities that needs to run on a highly constrained MCU.
Selecting the strategy that best meets the project's needs requires weighing the trade-offs.

 

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